Secrecy content of two-qubit states

Abstract

We analyze the set of two-qubit states from which a secret key can be extracted by single-copy measurements plus classical processing of the outcomes. We introduce a key distillation protocol and give the corresponding necessary and sufficient condition for positive key extraction. Our results imply that the critical error rate derived by Chau, Phys. Rev. A {\bf 66}, 060302 (2002), for a secure key distribution using the six-state scheme is tight. Remarkably, an optimal eavesdropping attack against this protocol does not require any coherent quantum operation.

5 pages, RevTeX

References in corpus (5)

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• Fidelity Bounds for Device-Independent Advantage Distillation
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• Bounds in Sequential Unambiguous Discrimination of Multiple Pure Quantum States
• Online identification of symmetric pure states
• Security of deterministic key distribution with higher-dimensional systems